The papaya mealybug, which excretes a sticky substance, infests a wide array of fruit and vegetable crops.

Courtesy of Jari Sugano

Q. Can you help me? I have this white sticky substance on the leaves and fruit of my papaya, tree and I don't know what it is.

A. Over the past few months, questions like this have become very common at county extension offices. The papaya mealybug (Paracoccus marginatus) was first detected on Maui in 2004 and has since spread to O'ahu, the Big Island and Kaua'i.

The papaya mealybug is known to infest a wide array of ornamental, fruit and vegetable crops. However, the preferred host plants are papaya, plumeria, hibiscus and jatropha.

Are the leaves on your papaya starting to crinkle and distort? Pests with sucking mouthparts like the papaya mealybug cause plants to discolor, twist and distort as they pierce through the plant's vascular tissue to extract sap. Yellowing, stunting and pre-mature fruit drop are the result of a reaction the plant has to a toxin that is injected by the papaya mealybug. Mealybugs are known to excrete a substance called honeydew. This substance causes a black, sooty mold to form on leaves and fruit. Plants covered with excessive amounts of sooty mold may eventually die due to the plant's inability to access sunlight and carry out photosynthesis.

Adult females of the papaya mealybug are wingless, oval in shape and have a yellow body. Males are smaller than the female. Males have wings, but only live for a few days. The eggs of the papaya mealybug are difficult to see as they are laid and covered in a white, cottony egg sac. The pest moves from plant to plant with the aid of wind, birds, humans and farm equipment.

What can you do to control this pest in your backyard? There are several nonchemical approaches you can take.

First, it is important to properly identify this pest before it becomes a major concern. Scout your yard for the papaya mealybug on susceptible host plants. If it is detected, spray a strong stream of water at the infected site and surrounding areas a couple of times a week. The stream of water will wash most of the immature mealybugs off the plant. Remove and bag infected plant materials and discard.

Minimizing insecticide applications may increase the population of some biological control insects that feed on the papaya mealybug. For example, a parasitic wasp known to attack the papaya mealybug is established on O'ahu, Maui and parts of the Big Island. These wasps are fairly specific in attacking the papaya mealybug and do not harm other plants and animals. In the long term, this may be the most practical way to control this pest.

For more information on how to manage the papaya mealybug, please contact the University of Hawai'i Master Gardener Hotline at 453-6055.

Jari Sugano and Steve Fukuda are extension agents with the University of Hawai'i-Manoa College of Tropical Agriculture and Human Resources. Reach Sugano at suganoj@ctahr.hawaii.edu.